Window Film for BTH

Today we learned that window film may do us some good at BTH, but PG&E won’t help us pay for it.

Well, today we learned that window film may do us some good at BTH, but PG&E won’t help us pay for it.

Paul Roman, Energy Specialist at Window Innovations, in Brentwood (925-766-6774), came over today on the recommendation of Richard Pon of PG&E. He spent about an hour meeting with BTH members from 2C, 5B, 8A, and 8D.

Here’s what we learned:

1. PG&E offers a rebate for window film for commercial accounts, but not for residential accounts. Window film could help us save natural gas, and our natural-gas account is classified as residential by PG&E, so there’s no rebate for us.

2. Window film could save us natural gas by trapping more heat indoors during cold weather, so our radiators don’t operate as much. However, all four attendees today testified that they never turn their radiators on. Film wouldn’t decrease the use of natural gas by anybody like us.

3. Window film could make us more comfortable and protect our furnishings by blocking some heat and almost all ultraviolet rays from coming in through our windows.

4. Window film would also protect us and our property against large sharp shards of glass in an earthquake by holding them all together instead of letting them fly through the air.

5. There is solar film, 1.5 mils thick, that incidentally provides shatter resistance. There is also safety film, 7–15 mils thick, that incidentally provides solar filtering. It seemed likely to me that most of us would prefer the former, if we chose to have film applied at all. The idea is that with light earthquake damage the thin film would suffice, and with heavy damage shattering windows would be the least of our worries.

6. Window Innovations recommended we consider three types of solar film, which it would be willing to supply and install for between $4.00 and $6.50 per square foot (no quantity discount). The less expensive film is somewhat more visible from the outside. The three films have somewhat different transmission and rejection properties. The bedroom window in 2C is 54 square feet in size, so applying film to it would cost between $216 and $351.

7. Roman left samples of these three types of film with me. I would be happy to show them to anybody at BTH.

8. Some lanai windows are insulated. Outdoor-side application of film tends to be kinder to insulated windows than indoor-side application, but the film doesn’t last as long when applied to the outdoor side. Window Innovations offers a “lifetime” warranty on films applied to the indoor sides and a 5-year warranty to films applied to the outdoor sides.

Susie has collected notes from several sources about this topic, and some of the sources advise safety film, or even laminated glass, rather than solar film for protection against shattering in earthquakes.

2 thoughts on “Window Film for BTH

  1. In reply to Mary Dean:

    When film is applied on the indoor side of insulated windows, the reflected solar heat becomes partly trapped inside the window and tends to accelerate the breakdown of the seal. Once the seal breaks, moisture gets in and clouds the window.

    My understanding from Roman was that the greatest range of solar filtering options and the greatest thermal efficacy are available with solar film.

    Since I wrote the initial report, long-time resident DP told me that the conventional wisdom predicted BTH would suffer primarily broken windows in a major earthquake, but that no BTH windows broke during the 1989 earthquake (only the first-floor suspended ceiling partly broke and fell to the floor). This might (just a guess) indicate that the potential stresses on BTH windows are sufficiently moderate so that the anti-shattering properties of solar film would suffice.

  2. Regarding film application to insulated lanai windows, in what way are they less kind when applied indoors?

    Do the safety film and solar film have equal solar filtering capacity?

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